I’ve shared this tip before, but I still get a lot of questions about how to view the Facebook chat windows in full screen.
Start by opening Facebook in your browser. Click the message icon at the top-right of the page.

Then choose See All in Messenger at the bottom of the menu that appears.

While the chat window doesn’t take up the full screen, it’s a good half of the screen and quite larger than that little chat box.

To find a friend, you can type their name at the left.

Just type your conversation in the center box and hit Send to send the message.

To go back to your Facebook feed, just click Home at the left

Thank you. It helped. So simple.
thank you, just what i wanted
First off the messenger icon is on my top left on the screen, not the right. Next I don’t get the “Send All In Messenger or Mark All As Read. Should I just dump the old messenger and start over?
Mike are you viewing in a browser on a PC or Mac?
Thank you CYNMACKLEY. I have no idea how the phrase “see all in messenger”” means “go to the full-screen version of messenger like they USED to have”. But it WORKS, and I would never have found it without your great explanation. Thanks very much!!
Oh my goodness – so simple! Thank you – and such a useful post, your URL came top of the list in a Google search for “how do you maximise the facebook messenger on desktop” 🙂